242 
THE PLANT WORLD. 
food. While the horse seizes his food with his lips, the cow, on 
the other hand, constantly makes use of the tongue in grazing. 
It shoots out from right or left and with a quick, sweeping, cir¬ 
cular motion draws the grass in. If a handfull of clover is held 
toward a hungry cow she will reach for it with extended tongue, 
which, if necessary, may be protruded several inches beyond the 
muzzle. The tip curves around the desired food and the rough 
surface helps to hold it. From constant use the tongue becomes 
a strong and adept organ of prehension. 
Fig. 50. The way in which Cock-spur Thorn is protected against brows¬ 
ing cattle. 
Now note that in browsing, when such an object as the de¬ 
pending branch of a tree is sought, the protruded tongue curves 
upward, and the branch is seized from beneath, as shown in our 
illustration (fig. 50). This is the habit of the deer, as well as of 
the ox, kind; and this observation makes it plain that the tend¬ 
ency of the spurs is a nice adaptation to their munitive function, 
with a view to the -foes to be feared and the quarter from which 
attack is to be expected. It is not unreasonable to surmise that 
had the browsing animals of northern temperate regions—the 
home of Crataegus —been of the horse kind, then the spurs of our 
plant would have pointed at all angles indifferently. 
As to the precise stimulus to which the general declination of 
the thorns is due, it is not easy to decide between gravity and 
